Fluorescent lamp coating



Patented Dec. '16, 1952 FLUORESCENT LAMP COATING John J. Benes, Jr., Geneva, 11]., assignor to (Jontinental Electric Company, Geneva, 111., a corporation of Delaware No Drawing. Application September 24, 1947, Serial No. 775,973

3 Claims.

This invention relates to improvements in fluorescent lamp coatings.

In the manufacture of fluorescent lamps filled with a small amount of mercury and with an inert gas, it has been experienced often that such lamps blacken during their life. This is especially pronounced in lamps that are made without electrodes to be placed in high frequency fields for charging the gaseous filling of the lamp. It appears that this blackening is due either to the action of mercury or to the fluorescent powders or to changes in such fluorescent powders under the impact of loaded particles.

The object of this invention is to improve the fluorescent lamp coatings and to prevent the blackening of the tubes in service.

I have discovered that fluorescent powders can be protected effectively during the life of the lamp or tube by depositing on the inner surface of the already coated tube a layer of a suitable silica, such as silicon oxide ($102) which is the result of the chemical breakdown of an ethyl silicate solution. According to the preferred embodiment of this invention, I prefer to proceed as follows:

A glass tube or lamp of the character desired, filled with an appropriate gas of the character customarily used in such lamps, is coated on the inside with a suitable luminescent or fluorescent material. One example thereof is a fluorescent material which will emit light when placed in a high frequency field, as provided by a fluorescent powder responsive to 2537 Angstrom radiation. This fluorescent powder is deposited on the inner wall of the glass tubing in a conventional way, such as by mixing, or in a solution containing nitro-cellulose, amyl acetate, and acetone. This coating preferably is baked at a temperature close to the softening point of the glass to remove the organic binder components.

The luminescent powders used may be of the character customarily employed in the trade, such as tungstates, silicates, or other materials generally used in low pressure mercury discharge fluorescent tubing.

The fluorescent tubing thus prepared as described above then may be treated to prevent blackening, according to the process of this invention. The coated tubing is then treated with a solution containing ethyl silicate, an example of which is as follows:

18 ml. 0.5% H01 26 ml. acetone 56 m1. ethyl silicate These parts are mixed together, preferably for about ten minutes, and then added to 400 ml. of acetone. This solution is then forced into the tube or lamp and coated over the fluorescent coating on the inner wall thereof, as by allowing it to drop thereon by gravity. The tubes then are dried in the air or may be heated, if desired, at 900 F. for approximately eight minutes, which heating has some advantage in the treatment.

Then the tubes may be used in the usual way of forming such fluorescent lamps by being evacuated, filled with an appropriate gas, etc. Then they may be used either with the usual electrodes or by energizing the fluorescent powders in high frequency fields, or in any other suitable manner.

It has been found that such tubes or lamps made according to the foregoing description, did not show blackening after a protracted period of time. This is believed to be due to the fact that the layer of silicon oxide transmits the 2537 Angstrom radiation generated in the tube, but protects the luminescent powder from the impact of high velocity charged particles.

The formula can be so adjusted or modified that the available silicon dioxide S102 from ethyl silicate will range from 1.0% to 25.0%.

While the invention has been illustrated and described in one embodiment, it is recognized that variations and changes may be made therein without departing from the invention, except as specified in the claims. It is understood particularly that the proportions given above and also the baking time and temperature can be varied in fairly wide limits to obtain the desired results.

I claim:

1. A process of treating lamps having a coating of fluorescent material on the inner wall thereof, comprising applying a solution of ethyl silicate, acetone and hydrochloric acid as a coating over the fluorescent coating, and heating said solution sufl'iciently to form a silica protective coating over the fluorescent material.

2. A process of treating lamps having a coating of fluorescent material on the inner wall thereof, comprising applying a coating comprising a solution of ethyl silicate, acetone and hydrochloric acid over the fluorescent coating, thereafter drying the lamp under a heat sufficient to convert the ethyl silicate to an oxide of silicon and evacuating and filling the same with a gas.

3. A process of treating lamps having a coating of fluorescent material on the inner wall thereof, comprising applying a liquid solution over the coating of fluorescent material, said solu- REFERENCES CITED P the followimg mgred1ents The following references are of record in the stan lally 1n hese proport ons. file of this patent:

18 ml. 0.5% HCl 26 m1. acetone a UNITED STATES PATENTS 56 m1. ethyl silicate Number Name Date 2,278,742 Scott Apr. '7, 1942 mixed with approximately 400 m1. of acetone 2,339,173 L m Jan, 11, 1944 and dryi sa d s lut 2,412,654 Sadowsky Dec. 17, 1946 JOHN J. BENES, JR. 10 2,451,590 Tidik 001;. 19, 1948 

1. A PROCESS OF TREATING LAMPS HAVING A COATING OF FLUORESCENT MATERIAL ON THE INNER WALL THEREOF, COMPRISING APPLYING A SOLUTION OF ETHYL SILICATE, ACETONE AND HYDROCHLORIC ACID AS A COATING OVER THE FLUORESCENT COATING, AND HEATING SAID SOLUTION SUFFICIENTLY TO FORM A SILICA PROTECTIVE COATING OVER THE FLUORESCENT MATERIAL. 